The 20-year-old singer enjoyed a night out with a group of friends and bodyguards at Guys & Dolls, where he stood up on a booth and got the crowd excited as he danced along to Michael Jackson's Dirty Diana, a source tells PEOPLE.

"He didn't seem to care at all that everyone was watching him," says the source. "He was in a totally good mood, just hanging out with his buddies. Then all of a sudden he decided to put on a little show. Everyone went wild."

Earlier that afternoon, a solemn Brown stood in a Los Angeles courtroom where a judge sentenced him to six months of community labor in Virginia (removing graffiti and washing cars), five years probation, a year of domestic violence classes and ordered him to not have any communication with Rihanna until 2014.